On an MPLS TE network, automatic bandwidth adjustment dynamically updates tunnel bandwidth upon service traffic changes, saving bandwidth resources.
MPLS TE tunnels are used to optimize traffic distribution over a network. Traffic that frequently changes wastes MPLS TE tunnel bandwidth; therefore, automatic bandwidth adjustment is used to prevent this waste. A bandwidth is initially set to meet the requirement for the maximum volume of services to be transmitted over an MPLS TE tunnel, to ensure uninterrupted transmission.
Automatic bandwidth adjustment allows a device to dynamically detect the traffic rate on a tunnel interface and periodically reestablish a tunnel based on the detection result and actual service bandwidth requirements.
Variable |
Notation |
Description |
|---|---|---|
Adjustment frequency |
A |
Interval at which bandwidth adjustment is performed. |
Sampling frequency |
B |
Interval at which traffic rates on a specific tunnel interface are sampled. The larger value between the mpls te timer auto-bandwidth command and the set flow-stat interval command is used. |
Actual bandwidth |
C |
The initial value is the configured tunnel bandwidth, and the subsequent value is the actual tunnel bandwidth. |
Target bandwidth |
D |
Updated bandwidth after adjustment. |
Threshold |
threshold |
An average bandwidth is calculated after the sampling interval time elapses. If the ratio of the difference between the average bandwidth and actual bandwidth to the actual bandwidth exceeds a specific threshold, automatic bandwidth adjustment is triggered. |
Samples traffic.
After automatic bandwidth adjustment is enabled on a tunnel interface, the ingress starts a bandwidth adjustment timer (A) and samples traffic at a specific interval (B seconds) to obtain the instantaneous bandwidth during each sampling period. The ingress records the instantaneous bandwidths for calculating the target bandwidth during automatic bandwidth adjustment.
Calculates an average bandwidth.
After timer A expires, the ingress uses the records to calculate an average bandwidth to be used as a target bandwidth (D).
If the device samples bandwidth values for less than two times within the specified interval, automatic bandwidth adjustment is not performed. The existing sampling times are counted in the next bandwidth adjustment interval.
Calculates a path.
The ingress runs CSPF to calculate a path with bandwidth D and establishes a new CR-LSP over that path.
Switches traffic to the new CR-LSP.
The ingress switches traffic to the new CR-LSP before tearing down the original CR-LSP. By now, the bandwidth adjustment in an interval is complete.
The preceding procedure repeats each time automatic bandwidth adjustment is triggered. Bandwidth adjustment is not needed if traffic fluctuates below a specific threshold. The ingress calculates an average bandwidth after the sampling interval time elapses. The ingress performs automatic bandwidth adjustment if the percentage of the difference between the average and existing bandwidths in the existing bandwidth exceeds a specific threshold. That is, [|(D - C)| ÷ C] × 100% > threshold. Otherwise, automatic bandwidth adjustment is not performed. This further optimizes the automatic bandwidth adjustment function.